ACTG 303 - The purpose of the study is to determine the influence of HIV virus load, characteristics of the virus and the presence of symptoms on response to new therapeutic regimens and on the development of viral resistance mutation in HIV infected individuals who have been treated with combination therapy on a previous ACTG trial. More specifically, this study will determine whether continuing ZDV/ddI, ZDV/ddC or adding 3TC or switching to ZDV/3TC will result in a more rapid or durable suppression of plasma viral RNA.